Motor, stator, and method for manufacturing stator

ABSTRACT

A stator having a stator core and coils is disclosed. The stator core includes split core pieces each having a tooth portion. The split core pieces are arranged annularly such that the distal ends of the tooth portions face radially inward. A lead wire is continuously wound about an adjacent pair of the tooth portions such that coils of different phases are formed in the circumferentially adjacent tooth portions, so that a plurality of connecting wires are provided, each connecting wire connecting coils of different phases. The connecting wires are connected to one another while being connected to one another, such that a neutral point is created.

The present invention relates to a motor, a stator, and a method formanufacturing a stator.

BACKGROUND OF THE INVENTION

Conventionally, the stator of an inner rotor type motor has an annularstator core and coils. The stator core has tooth portions extendingradially on the radially inner side of the stator, and the coils arewould about the tooth portions. Japanese Laid-Open Patent PublicationNo. 11-18345 discloses a stator having a split core that is divided intopieces each corresponding to one tooth portion. A stator having a splitcore is spread flat when coils are wound about the tooth portions. Then,the split core pieces are annularly arranged such that the toothportions are oriented radially inward, so that the stator is formed. Ina stator having a split core, coils are wound about tooth portions withthe stator being spread flat. This increases the space factor of thecoils.

In the stator disclosed in Japanese Laid-Open Patent Publication No.11-18345, a single lead wire is wound about each tooth portion. However,in the stator of Japanese Laid-Open Patent Publication No. 11-18345,both ends of every coil (lead wire) need to be connected to apredetermined conductive member, which complicates the wire connectingprocedure.

As a technique for remedying the above drawback, the stator disclosed byJapanese Laid-Open Patent Publication No. 2002-176753 has aconfiguration in which a plurality of coils of the same phase are formedby a single lead wire, and a connecting wire extends between the coils.Each lead wire that constitutes the coils of one phase is connected atone end to a common neutral point, and receives at the other end thesupply of alternating current of a 120 degree phase difference. Sincethis structure allows the number of the lead wires forming the coils tobe less than the number of the tooth portions, the number ofmanufacturing steps for the lead wire connecting procedure of the endsof the wires is reduced.

However, in the stator of Japanese Laid-Open Patent Publication No.2002-176753, coils of the same phase are arranged in the circumferentialdirection with a coil of another phase in between. This makes theconnecting wire between the coils of the same phase relatively long.Therefore, in a circularization process of the stator and a connectingprocess that is performed after the circularization process to connectconnecting wires, the connecting wires are likely to get entangled,making these processes troublesome. Also, in a stator having a splitcore, the stator is made annular from a spread flat state after coilsare wound about the tooth portions. The length of each connecting wiretherefore needs to have a sufficient margin. In other words, the lengthof the connecting wires need to be set relatively long.

SUMMARY OF THE INVENTION

Accordingly, it is an objective of the present invention to provide amotor, a stator, and a method for manufacturing a stator that shortenthe length of wires and prevent connecting wires from getting entangled.

To achieve the foregoing objective and in accordance with a first aspectof the present invention, a stator including a stator core and aplurality of coils is provided. The stator core includes a plurality ofsplit core pieces each having a tooth portion. The split core pieces areannularly arranged such that distal ends of the tooth portions faceradially inward. Each of the coils is wound about one of the toothportions, the coils are divided into groups of n phases. A lead wire iscontinuously wound about an adjacent pair of the tooth portions suchthat coils of different phases are formed in the circumferentiallyadjacent tooth portions, so that a plurality of connecting wires areprovided. Each connecting wire connects coils of different phases.Either the connecting wires are connected to each other or theconnecting wires are connected to each other in a state where at leastone of the connecting wires is cut, such that a neutral point iscreated.

In accordance with a second aspect of the present invention, a motorhaving an annular stator fixed to an inner circumferential surface of acylinder shaped like a bottomed cylinder, a rotor rotatably arrangedinside the stator, and a holder member located at an opening of thehousing is provided. The holder member covers one end of the stator inthe axial direction. The stator includes a stator core and a pluralityof coils. The stator core has a plurality of split core pieces eachhaving a plurality of tooth portions. The split core pieces areannularly arranged such that distal ends of the tooth portions faceradially inward. The coils are each wound about one of the toothportions and include a U-phase coil, a V-phase coil, and a W-phase coil.A lead wire is continuously wound about an adjacent pair of the toothportions such that coils of different phases are formed in thecircumferentially adjacent tooth portions, so that a plurality ofconnecting wires are provided. Each connecting wire connects coils ofdifferent phases. Either the connecting wires are connected to eachother or the connecting wires are connected to each other in a statewhere at least one of the connecting wires is cut, such that a neutralpoint is created. The connecting wires include a U-phase-to-V-phaseconnecting wire connecting the U-phase coil and the V-phase coil, aV-phase-to-W-phase connecting wire connecting the V-phase coil and theW-phase coil, and a W-phase-to-U-phase connecting wire connecting theW-phase coil and the U-phase coil. At least one of the connecting wiresis formed into a ring along the circumferential direction of the stator.

In accordance with a third aspect of the present invention, a method formanufacturing a stator is provided. The stator has a stator core and aplurality of coils. The stator core includes a plurality of split corepieces each having a tooth portion. The split core pieces are annularlyarranged such that distal ends of the tooth portions face radiallyinward. The coils are each wound about one of the tooth portions, andare divided into groups of n phases. The method includes: winding a leadwire about each adjacent pair of the tooth portions with the toothportions are spread such that the distal ends of the tooth portions areseparated from on another, such that coils of different phases areprovided on each adjacent pair of the tooth portions, wherein aconnecting wire connects the coils of the different phases; making thespread stator core have an annular shape such that the distal ends ofthe tooth portions face radially inward; and connecting the connectingwires, each of which connects coils of different phases wound aboutcircumferentially adjacent tooth portions, to each other.

Other aspects and advantages of the present invention will becomeapparent from the following description, taken in conjunction with theaccompanying drawings, illustrating by way of example the principles ofthe invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention, together with objects and advantages thereof, may best beunderstood by reference to the following description of the presentlypreferred embodiments together with the accompanying drawings in which:

FIG. 1A is a cross-sectional view of a brushless motor according to oneembodiment;

FIG. 1B is a plane view of the brushless motor of FIG. 1A;

FIG. 2A is a plan view of a stator of the present embodiment;

FIG. 2B is a cross-sectional view of the stator;

FIG. 3 is a diagrammatic plan view for explaining a connecting wirebetween different phases;

FIG. 4 is a wiring diagram of coils;

FIG. 5A is a cross-sectional view for explaining a joint portion ofconnecting wires;

FIG. 5B is a side view for explaining a joint portion of connectingwires;

FIG. 6 is a perspective view illustrating the stator after acircularization process;

FIG. 7A is a perspective view showing a film removal process;

FIG. 7B is a perspective view showing a joining process;

FIG. 7C is a perspective view showing the joining process;

FIG. 8 is a cross-sectional view for explaining a manner in whichconnecting wires are joined according to a modified embodiment;

FIG. 9 is a cross-sectional view for explaining a manner in whichconnecting wires are joined according to a modified embodiment;

FIG. 10 is a diagrammatic plan view illustrating a stator according to amodified embodiment;

FIG. 11 is a diagrammatic plan view illustrating a stator according to amodified embodiment;

FIG. 12 is a diagrammatic plan view illustrating a stator according to amodified embodiment;

FIG. 13 is a diagrammatic plan view illustrating a stator according to amodified embodiment;

FIG. 14 is a diagrammatic plan view illustrating a stator according to amodified embodiment;

FIG. 15 is a diagrammatic plan view illustrating a stator according to amodified embodiment; and

FIG. 16 is a diagrammatic cross-sectional view illustrating a connectingmember according to a modified embodiment.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, a preferred embodiment according to the present inventionwill be described.

A brushless motor 1 shown in FIGS. 1A and 1B is used as a drive sourceof a power steering apparatus that assists the operation of a vehiclesteering shaft coupled to a vehicle steering wheel (not shown). As shownin FIGS. 1A and 1B, the motor 1 has a housing 2 shaped as a bottomedcylinder, and a substantially cylindrical stator 3 is fixed to the innercircumferential surface of the housing 2. The rotor 4 is rotatablyarranged in the stator 3. The rotor 4 is coupled to the unillustratedvehicle steering shaft. A holder member 5, which is made of insulatingsynthetic resin, is fixed to an end of the housing 2 of the stator 3 atan opening 2 a. The holder member 5 covers one end of the stator 3 inthe axial direction.

As shown in FIG. 2A, a stator core 6 of the stator 3 includes aplurality of annularly arranged split core pieces 7 and coupling members9 each of which couples the radially outer ends of a circumferentiallyadjacent pair of the split core pieces 7. The stator core 6 issubstantially annular. In the present embodiment, the number of thesplit core pieces 7 is twelve. Each split core piece 7 has a toothportion 8 that extends radially inward in the stator 3. The toothportions 8 are arranged at equal intervals in the circumferentialdirection. In the present embodiment, the tooth portions 8 are providedevery 30°. For purposes of illustration, a tooth portion 8 at a bottomright position of the stator 3 shown in FIG. 2A is expressed byreference numeral 8 a, and the tooth portions 8 arranged clockwise fromthe tooth portion 8 a is successively given reference numerals 8 b to 8l.

As shown in FIG. 2B, a bobbin 10 is attached to each of the toothportions 8 a to 8 l, to cover the ends in the axial direction and thesides in the circumferential direction. A coil C is wound about eachbobbin 10. The coils C are divided into four U-phase coils U1 to U4,four V-phase coils V1 to V4, and four W-phase coils W1 to W4 incorrespondence with three drive currents of supplied in three-phases(U-phase, V-phase, and W-phase).

Two of the four coils in each single phase are wound aboutcircumferentially adjacent two tooth portions 8, respectively. The othertwo coils are wound about two tooth portions 8, each spaced by 180° fromone of the first two coils. Specifically, the V-phase coils, V2, V1, theU-phase coils U4, U3, the W-phase coils W3, W4, the V-phase coils V3,V4, the U-phase coils U1, U2, and the W-phase coils W2, W1 aresequentially wound about the tooth portions 8 a to 8 l, respectively, inthe clockwise direction.

The twelve coils U1 to W4 are formed by three lead wires wound about thetooth portions 8 by way of concentrated winding, that is, a first leadwire 11, a second lead wire 12, and a third lead wire 13. FIG. 4 is awiring diagram schematically showing the manner in which the first tothird lead wires 11 to 13 are wound. In FIG. 4, the coils C are shown inthe order from the left from the V-phase coil V2 to the W-phase coil W1.As shown in FIG. 4, the first lead wire 11 forms the V-phase coils V2,V1 and the U-phase coils U4, U3, the second lead wire 12 forms theW-phase coils W3, W4 and the V-phase coils V3, V4, and the third leadwire 13 forms the U-phase coils U1, U2 and the W-phase coils W2, W1.That is, each of the first to third lead wires 11 to 13 is wound aboutcircumferentially consecutive four of the tooth portions 8. As shown inFIG. 5A, each of the lead wires 11 to 13 is a metal wire coated withinsulating coating, and has a circular cross-section. In the presentembodiment, the lead wires 11 to 13 are formed of copper.

The first lead wire 11 is wound in a forward direction about the toothportion 8 a (in the present embodiment, wound counterclockwise whenviewed from the distal end of the tooth portion 8 a, that is, whenviewed from the inner end in the radial direction). The first lead wire11 is drawn to the tooth portion 8 b, which is adjacent to the toothportion 8 a, and is wound in a reverse direction about the tooth portion8 b (in this present embodiment, wound clockwise when viewed from thedistal end of the tooth portion 8 b, that is, when viewed from the innerend in the radial direction. In this manner, the V-phase coils V2, V1are wound about the tooth portions 8 a, 8 b, respectively. The head ofthe first lead wire 11 extends from the V-phase coil V2 toward theholder member 5. A part of the first lead wire 11 that extends from theV-phase coil V2 forms a first V-phase power line 11 a. A same phaseconnecting wire 14 extending between the V-phase coil V1 and the V-phasecoil V2 is formed at an end of the stator 3 opposite from the holdermember 5.

Also, the first lead wire 11 is drawn from the tooth portion 8 b to theadjacent tooth portion 8 c to be wound in the forward direction aboutthe tooth portion 8 c, and drawn to the adjacent tooth portion 8 d to bewound in the reverse direction about the tooth portion 8 d. In thismanner, the U-phase coils U4, U3 are wound about the tooth portions 8 c,8 d, respectively. The tail of the first lead wire 11 extends from theU-phase coil U3 in the same direction as the first V-phase power line 11a, that is, extends toward the holder member 5. The tail of the firstlead wire 11 forms a first U-phase power line 11 b. A U-phase-to-V-phaseconnecting wire 11 c (a drawn wire) extending between the V-phase coilV1 and the adjacent U-phase coil U4 extends in the same direction as thefirst V-phase power line 11 a and the first U-phase power line 11 b. Asame phase connecting wire 14 extending between the U-phase coil U4 andthe U-phase coil U3 is formed at an end of the stator 3 opposite fromthe U-phase-to-V-phase connecting wire 11 c, that is, from the holdermember 5 in the stator 3.

The second lead wire 12 is wound about the tooth portions 8 e to 8 hsubstantially in the same manner as the first lead wire 11. The secondlead wire 12 forms the W-phase coils W3, W4 and the V-phase coils V3, V4wound about the tooth portions Se to 8 h. The length of aV-phase-to-W-phase connecting wire 12 c (a drawn wire) between theW-phase coil W4 and the adjacent V-phase coil V3 is shorter than that ofthe U-phase-to-V-phase connecting wire 11 c. As shown in FIG. 3, theV-phase-to-W-phase connecting wire 12 c is arched to be slightlyseparated from an end face 3 a in the axial direction of the stator 3.

The third lead wire 13 is wound about the tooth portions 8 i to 8 l inthe same manner as the second lead wire 12. The third lead wire 13 formsthe U-phase coils U1, U2 and the W-phase coils W2, W1 wound about thetooth portions 8 i to 8 l. That is, the length of a W-phase-to-U-phaseconnecting wire 13 c (a drawn wire) between the U-phase coil U2 and theadjacent W-phase coil W2 is equal to that of the V-phase-to-W-phaseconnecting wire 12 c of the second lead wire 12. The W-phase-to-U-phaseconnecting wire 13 c is also arched to be slightly separated from theaxial end face 3 a of the stator 3.

As shown in FIG. 2B, the U-phase-to-V-phase connecting wire 11 c of thefirst lead wire 11 is bent substantially at a right angle in a proximalportion close to the V-phase coil V1 and the U-phase coil U4, andextends along the axial end face 3 a of the stator 3. That is, theU-phase-to-V-phase connecting wire 11 c is bent to be substantiallyparallel with the axial end face 3 a of the stator 3. As shown in FIG.3, the U-phase-to-V-phase connecting wire 11 c conforms to the annularshape of the stator 3, or extends along the circumferential direction ofthe stator 3. The U-phase-to-V-phase connecting wire 11 c is formed intoa ring having a diameter that is not smaller than the inner diameter andnot greater than the outer diameter of the stator 3. The thus configuredU-phase-to-V-phase connecting wire 11 c has a required minimum lengthfor being connected to the V-phase-to-W-phase connecting wire 12 c andto the W-phase-to-U-phase connecting wire 13 c. The U-phase-to-V-phaseconnecting wire 11 c is connected to the V-phase-to-W-phase connectingwire 12 c and the W-phase-to-U-phase connecting wire 13 c by connectingmembers 15. The V-phase-to-W-phase connecting wire 12 c and theW-phase-to-U-phase connecting wire 13 c each have a sufficient lengthfor being connected to the U-phase-to-V-phase connecting wire 11 c, andis formed to extend substantially parallel with the axial end face 3 aof the stator 3.

As shown in FIGS. 5A and 5B, each connecting member 15 is formed bypressing a metal plate. Each connecting member 15 has integrally formedtwo arcuate portions 15 a, which can be brought into an area contactwith the surfaces of the connecting wires 11 c, 12 c, 13 c. Each arcuateportion 15 a has a semicircular cross section. A retaining claw 15 b isformed at the open end of each arcuate portion 15 a in thecircumferential direction. Each retaining claw 15 b serves as aretaining portion that projects in the circumferential direction. TheU-phase-to-V-phase connecting wire 11 c is fitted in one of the twoarcuate portions 15 a, and the V-phase-to-W-phase connecting wire 12 cor the W-phase-to-U-phase connecting wire 13 c is fitted in the otherarcuate portion 15 a. The U-phase-to-V-phase connecting wire 11 c iselectrically connected to the V-phase-to-W-phase connecting wire 12 cand the W-phase-to-U-phase connecting wire 13 c by the connectingmembers 15, so that neutral points is created. The retaining claws 15 bprevent the connecting wires 11 c, 12 c, 13 c from separating from thearcuate portions 15 a.

As shown in FIGS. 1A and 1B, the holder member 5 includes an outercylindrical portion 5 b and an inner cylindrical portion 5 c. The outercylindrical portion 5 b extends axially from an annular bottom portion 5a of the holder member 5 and is fixed to the inner circumferentialsurface of the housing 2. The inner cylindrical portion 5 c extends in aposition radially inside of the outer cylindrical portion 5 b. Anaccommodation recess 5 d extending along the axial direction is definedbetween the outer cylindrical portion 5 b and the inner cylindricalportion 5 c. The accommodation recess 5 d accommodates theU-phase-to-V-phase connecting wire 11 c, the V-phase-to-W-phaseconnecting wire 12 c, and the W-phase-to-U-phase connecting wire 13 c,which are connected to one another. The holder member 5 also has threeincisions 5 e extending in the radial direction. Each incision 5 e holdsone of feed terminals 21 a, 21 b, 21 c each corresponding to one of thedrive currents of three phases.

The first V-phase power line 11 a drawn from the V-phase coil V2 extendsalong the circumferential direction of the stator 3 until it reaches asecond V-phase power line 12 b drawn from the V-phase coil V4 (the tailof the second lead wire 12). As shown in FIG. 1B, each of the V-phasepower lines 11 a, 12 b is electrically connected to the feed terminal 21a, for example, by TIG welding. The first U-phase power line 11 b drawnfrom the U-phase coil U3 (the tail of the first lead wire 11) extendsalong the circumferential direction of the stator 3 until it reaches asecond U-phase power line 13 a drawn from the U-phase coil U1 (the headof the third lead wire 13). As shown in FIG. 1B, each of the U-phasepower lines 11 b, 13 a is electrically connected to the feed terminal 21b, for example, by TIG welding. A first W-phase power line 12 a drawnfrom the W-phase coil W3 (the head of the second lead wire 12) and asecond W-phase power line 13 b drawn from the W-phase coil W1 (the tailof the third lead wire 13) each extend until it reaches a positionslightly closer to the U-phase coil U1 than the U-phase coil U2. TheW-phase power line 12 a, 13 b are each electrically connected to thefeed terminal 21 c, for example, by TIG welding. Each of the power lines11 a to 13 b receives drive current of the corresponding phase throughthe feed terminals 21 a, 21 b, 21 c.

As shown in FIG. 1A, a rotary shaft 31 of the rotor 4 is supported by apair of bearings 32 (only one is shown) provided in the housing 2. Acylindrical rotor core 33 is fixed to the rotary shaft 31, and a magnet34 is fixed to the outer circumferential surface of the rotor core 33.The magnet 34 is polarized such that the polarity varies alternately(between north pole and south pole) every predetermined angle.

In the brushless motor 1 as described above, three drive currents having120° degree phase differences are supplied to the coils U1 to W4 throughthe feed terminals 21 a, 21 b, 21 c. Then, each of the coils U1 to W4 isexcited to generate a rotating magnetic field in the stator, which inturn rotates the rotor 4.

The method for manufacturing the above described stator 3 will now bedescribed.

First, the split core pieces 7 are linearly arranged to be parallel withthe tooth portions 8, and the stator core 6 is spread flat. In thisspread flat state, the split core pieces 7 are pivotally connected toeach other at the radially outer ends by the coupling members 9. In thespread flat state, a winding process is executed, in which the coils U1to W4 are wound about the tooth portions 8.

In the winding process, the first to third lead wires 11 to 13 are woundabout the tooth portions 8 by way of concentrated winding in the mannerdescribed above, using a coil winding machine (not shown). The firstlead wire 11 is wound about the tooth portions 8 a to 8 d. Then, thesecond lead wire 12 is wound about the tooth portions 8 e to 8 h.Thereafter, the third lead wire 13 is wound about the tooth portions 8 ito 8 l. At this time, the U-phase-to-V-phase connecting wire 11 c isdrawn to have a length sufficient for being connected to theV-phase-to-W-phase connecting wire 12 c and to the W-phase-to-U-phaseconnecting wire 13 c. Also, the V-phase-to-W-phase connecting wire 12 cand the W-phase-to-U-phase connecting wire 13 c are each arched to beslightly separated from the axial end face 3 a of the stator 3 andcaused to project from the axial end face 3 a. In the winding process,the first to third lead wires 11 to 13 may be simultaneously wound aboutthe tooth portions.

Then, a circularization process is executed, in which the spread flatstator 3 is rolled up such that the distal ends of the tooth portions 8a to 8 l face radially inward. Through the circularization process, thestator 3 is in the state shown in FIG. 6. In the present embodiment, theconnecting wires of the stator 3 (the phase-to-phase connecting wires 11c, 12 c, 13 c and the same phase connecting wire 14) all extend over anadjacent pair of the coils U1 to W4. Thus, the connecting wires can bemade short. This configuration prevents the connecting wires fromgetting entangled in the circularization process. As a result, thecircularization process of the stator 3 is facilitated.

A connecting wire forming process is then executed, in which theU-phase-to-V-phase connecting wire 11 c is formed into a predeterminedshape. In the connecting wire forming process, the U-phase-to-V-phaseconnecting wire 11 c is formed into a ring along the circumferentialdirection of the stator 3. Thereafter, the U-phase-to-V-phase connectingwire 11 c is bent substantially at a right angle to be substantiallyparallel with the axial end face 3 a of the stator 3. In this processalso, the connecting wires of the stator 3 all extend over an adjacentpair of the coils U1 to W4. This configuration prevents the connectingwires from getting entangled and thus facilitates the production of theU-phase-to-V-phase connecting wire 11 c.

Next, a film removal process for removing films on predetermined partsof the connecting wires 11 c, 12 c, 13 c is performed. As shown in FIG.7A, in the film removal process, laser beam is radiated to the axial endface 3 a of the stator 3 from a laser beam device (not shown), such thatthe laser beam is radiated to a portion of the connecting wires 11 c, 12c, 13 c on a side of the stator 3 opposite from the axial end face 3 a.This removes the film on the parts of the connecting wires 11 c, 12 c,13 c to which the laser beam has been radiated, so that film freeportions R are formed on the connecting wires 11 c, 12 c, 13 c.

Next, a joining process is executed, in which the connecting wires 11 c,12 c, 13 c are electrically connected to each other via the connectingmembers 15. In the joining process, each connecting member 15 is placedon the film free portions R of the corresponding pair of the connectingwires 11 c, 12 c, 13 c as shown in FIG. 7B. At this time, theU-phase-to-V-phase connecting wire 11 c is fitted in one of the twoarcuate portions 15 a of each connecting member 15, and theV-phase-to-W-phase connecting wire 12 c or the W-phase-to-U-phaseconnecting wire 13 c is fitted in the other arcuate portion 15 a. Thisbrings the inner surface of each arcuate portion 15 a into area contactwith the corresponding film free portion R.

Next, as shown in FIG. 7C, each connecting member 15 is joined to thecorresponding pair of the connecting wires 11 c, 12 c, 13 c by laserwelding. In the welding process, the laser beam that is radiated towardthe axial end face 3 a of the stator 3 is radiated to the upper surfaceof the arcuate portions 15 a. The laser beam forms a through hole ineach arcuate portion 15 a, so that the inner surface of the arcuateportion 15 a is welded to the upper surface of the corresponding one ofthe connecting wires 11 c, 12 c, 13 c. That is, a joint portion P atwhich each connecting member 15 is welded to the connecting wires 11 c,12 c, 13 c is formed in a position of the stator 3 opposite from theaxial end face 3 a (see FIGS. 2A, 2B, 5A, and 5B). In this manner, theU-phase-to-V-phase connecting wire 11 c is electrically connected to theV-phase-to-W-phase connecting wire 12 c and to the W-phase-to-U-phaseconnecting wire 13 c.

The direction of radiation of the laser beam in the welding process isthe same as the direction of radiation of the laser beam in the filmremoval process. It is therefore possible to use the same laser beamdevice used in the film removal process.

As described above, in the stator 3 of the present embodiment, the jointportion P between each connecting member 15 and the connecting wires 11c, 12 c, 13 c are formed at a position of the stator 3 opposite from theaxial end face 3 a. This allows the connecting wires 11 c, 12 c, 13 c tobe welded while being maintained parallel with the axial end face 3 a ofthe stator 3. This eliminates the necessity for a process to extend theconnecting wires 11 c, 12 c, 13 c along the axial direction. Also, sincethe connecting wires 11 c, 12 c, 13 c do not need to be welded whilebeing extended, the joint between the connecting wires 11 c, 12 c, 13via the connecting members 15 is facilitated. Since the connecting wires11 c, 12 c, 13 c are substantially parallel with the axial end face 3 aof the stator 3, the axial length of the entire stator 3 is reduced.Further, since the joint portions P do not face the coils C, thereliability of insulation between the connecting wires 11 c, 12 c, 13 cand the coils C is improved.

After the joining process, the connecting wires 11 c, 12 c, 13 c arearranged at the positions shown in FIG. 3. Then, the power lines 11 a to13 b are formed to be in the above described state, and arranged atpositions corresponding to the feed terminals 21 a, 21 b, 21 c in theholder member 5. Thereafter, the power lines 11 a to 13 b are drawn toradially outside.

Then, the stator 3, which has been produced in the above describedmanner, is installed in the housing 2. Thereafter, the holder member 5is assembled with the housing 2, so that the connecting wires 11 c, 12c, 13 c are accommodated in the accommodation recess 5 d of the holdermember 5. Then, each of the power lines 11 a to 13 b are passed throughthe corresponding incision 5 e of the holder member 5, and iselectrically connected to the feed terminal 21 a to 21 c of thecorresponding phase.

The present embodiment has the following advantages.

(1) In the brushless motor 1 of the present embodiment, coils U1 to W4of different phases are continuously wound about circumferentiallyadjacent ones of the tooth portions 8, and the U-phase-to-V-phaseconnecting wire 11 c, the V-phase-to-W-phase connecting wire 12 c, andthe W-phase-to-U-phase connecting wire 13 c are provided to connect thecoils U1 to W4 of different phases. The connecting wires 11 c, 12 c, 13c are connected to each other to form the neutral points. Since each ofthe phase-to-phase connecting wires 11 c, 12 c, 13 c is formed betweencircumferentially adjacent coils U1 to W4, the length of the connectingwires 11 c, 12 c, 13 c are made short. Since the connecting wires areprevented from getting entangled in the circularization process of thestator 3 and the subsequent process for connecting the connecting wires,the stator 3 is easily produced. Since the first to third lead wires 11to 13 do not need to be long, the configuration contributes to thereduction in the costs.

(2) In the present embodiment, the U-phase-to-V-phase connecting wire 11c is formed into a ring conforming to the annular shape of the stator 3.This allows the length of the phase-to-phase connecting wires 11 c, 12c, 13 c to be minimized. As a result, the connecting wires 11 c, 12 c,13 c are reliably prevented from getting entangled in thecircularization process and the joining process.

(3) In the present embodiment, the connecting wires 11 c, 12 c, 13 c areformed to be parallel with the axial end face 3 a of the stator 3. Theconnecting wires 11 c, 12 c, 13 c are joined to each other through theconnecting members 15 by welding. The joint portions P between theconnecting members 15 and the connecting wires 11 c, 12 c, 13 c arelocated on part of the stator 3 opposite from the axial end face 3 a.Therefore, the connecting wires 11 c, 12 c, 13 c can be welded whilebeing bent to be substantially parallel with the axial end face 3 a ofthe stator 3. As a result, a process for extending the connecting wires11 c, 12 c, 13 c along the axial direction is unnecessary. Also, theconnecting wires 11 c, 12 c, 13 c do not need to be welded while beingextended. This facilitates the joint of the connecting wires 11 c, 12 c,13. Since the connecting wires 11 c, 12 c, 13 c are substantiallyparallel with the axial end face 3 a of the stator 3, the axial lengthof the entire stator 3 is reduced. Further, since the joint portions Pare formed at part of the stator 3 opposite from the axial end face 3 a,the joint portions P do not face the coils C, and the reliability ofinsulation between the connecting wires 11 c, 12 c, 13 c and the coils Cis improved.

(4) In the present embodiment, the connecting wires 11 c, 12 c, 13 c areelectrically connected to each other through the connecting members 15,and the joint portions P are formed between the connecting wires 11 c,12 c, 13 c and the connecting member 15. This reinforces the joint ofconnecting wires 11 c, 12 c, 13 c.

(5) In the present embodiment, since the connecting members 15 have thearcuate portions 15 a that are in area contact with and welded to theconnecting wires 11 c, 12 c, 13 c, the reliability of the joint betweenthe connecting wires 11 c, 12 c, 13 c and the connecting members 15 isimproved.

(6) In the present embodiment, each connecting member 15 has retainingclaws 15 b, which prevent the connecting wires 11 c, 12 c, 13 c fromseparating from the arcuate portions 15 a.

(7) In the present embodiment, the connecting wires 11 c, 12 c, 13 c arewelded to the connecting members 15 by laser welding within a very shorttime. Thus, the thermal influence on parts about the connecting wires 11c, 12 c, 13 c, for example, members such as the coils C, is reduced.Since laser beam can be used to weld the connecting wires 11 c, 12 c, 13c to part of the stator 3 opposite from the axial end face 3 a, thecoils C, which are wound about tooth portions 8 located on the axial endface 3 a of the stator 3, is not damaged. Accordingly, the coils C andthe connecting wires 11 c, 12 c, 13 c can be arranged to close to eachother in the axial direction. This reduces the axial length of thestator 3. Further, when the laser welding is employed, no electrodeneeds to be placed between the coils C and the connecting wires 11 c, 12c, 13 c. This further reduces the axial length of the stator 3.

(8) Since the U-phase-to-V-phase connecting wire 11 c is formed into aring along the circumferential direction of the stator 3, the connectingwires 11 c, 12 c, 13 c are easily joined together.

(9) In the present embodiment, the coils C are formed by metal wirescoated with insulating coating, and the connecting wires 11 c, 12 c, 13c are parts the coated lad wire drawn out of the coils C. In the filmremoval process, laser beam is radiated onto parts of the connectingwires 11 c, 12 c, 13 c opposite from the axial end face 3 a of thestator 3, so that the film free portions R are formed. Thereafter, inthe joining process, the film free portions R of the connecting wires 11c, 12 c, 13 c are welded to form the joint portions P. That is, the filmon the coils C is removed in advance by radiating the laser beam thereonbefore the connecting wires 11 c, 12 c, 13 c are welded to theconnecting members 15. This improves the reliability of the electricconnection at the joint portions P between the connecting members 15 andthe connecting wires 11 c, 12 c, 13 c. Also, subsequent to the filmremoval, laser beam is radiated from the same direction to weld theconnecting wires 11 c, 12 c, 13 c to the connecting members 15.Therefore, the laser facilities do not need to be moved and the numberof manufacturing steps is reduced. As a result, it is possible toprovide an inexpensive stator 3.

(10) In the present embodiment, since the U-phase-to-V-phase connectingwire 11 c is formed into a ring along the circumferential direction ofthe stator 3, the connecting wires 11 c, 12 c, 13 c are easily joinedtogether. Since the length of the phase-to-phase connecting wires 11 c,12 c, 13 c can be minimized, the connecting wires 11 c, 12 c, 13 c aremore effectively prevented from getting entangled.

(11) In the present embodiment, when winding the coils C of differentphases about adjacent ones of the tooth portions 8, the connecting wires11 c, 12 c, 13 c are arched and projected from the axial end face 3 a ofthe stator 3. Therefore, the arched connecting wires 11 c, 12 c, 13 care easily formed, and an inexpensive stator 3 can be provided.

The above embodiment of the present invention may be modified asfollows.

As shown in FIG. 8, the connecting wires 11 c, 12 c, 13 c may bedirectly joined to each other. In this case, a holder 20 shown in FIG. 9may be provided under the connecting wires 11 c, 12 c, 13 c, that is, onthe axial end face 3 a of the stator 3. The holder 20 holds the joinedconnecting wires 11 c, 12 c, 13 c. This structure improves thereliability of the joint between the connecting wires 11 c, 12 c, 13 c.

As shown in FIG. 10, two wire segments 41 may be provided by cutting theU-phase-to-V-phase connecting wire 11 c. One of the wire segments 41 maybe connected to the V-phase-to-W-phase connecting wire 12 c, and theother may be connected to the W-phase-to-U-phase connecting wire 13 c.The connecting wire that is cut may be any of the connecting wires 11 c,12 c, 13 c. Also, two or all of the connecting wires 11 c, 12 c, 13 cmay be cut. These structures further shorten the phase-to-phaseconnecting wires.

The manner in which the connecting wires 11 c, 12 c, 13 c are connectedis not limited to that disclosed in the above embodiment. For example, aV-phase-to-W-phase connecting wire 51 shown in FIG. 11 is may be used.The V-phase-to-W-phase connecting wire 51 is arched and extends alongthe circumferential direction of the stator 3 to a U-phase-to-V-phaseconnecting wire 52. That is, a part drawn from the V-phase coil V3 and apart drawn from the W-phase coil W4 both extend along thecircumferential direction of the stator 3. The V-phase-to-W-phaseconnecting wire 51 is connected to the U-phase-to-V-phase connectingwire 52 via the connecting members 15. An W-phase-to-U-phase connectingwire 53 is arched and entirely extends along the circumferentialdirection of the stator 3 to the V-phase-to-W-phase connecting wire 51.The W-phase-to-U-phase connecting wire 53 is connected to theV-phase-to-W-phase connecting wire 51 via the connecting members 15.This structure also shortens the circumferential measurement of theconnecting wires 51, 52, 53, thereby preventing the connecting wires 51,52, 53 from getting entangled. This facilitates the connection of theconnecting wires 51, 52, 53.

Like the V-phase-to-W-phase connecting wire 51 and theW-phase-to-U-phase connecting wire 53, the U-phase-to-V-phase connectingwire 52 may be arched and entirely extend along the circumferentialdirection of the stator 3 to the W-phase-to-U-phase connecting wire 53,and may be connected to the W-phase-to-U-phase connecting wire 53 asshown in FIG. 12. Also, as shown in FIG. 13, the W-phase-to-U-phaseconnecting wire 53 may be arched and entirely extend along thecircumferential direction of the stator 3 to an U-phase-to-V-phaseconnecting wire 52, so as to be connected to the U-phase-to-V-phaseconnecting wire 52. The connecting wires 51, 52, 53 are connected toeach other by connecting members 54. The structures shown in FIG. 12 andFIG. 13 facilitate the connection of the connecting wires 51, 52, 53.The structure shown in FIG. 13 reduces the number of components in acase where connecting wires are connected via connecting members.

Instead of the U-phase-to-V-phase connecting wire 11 c, theV-phase-to-W-phase connecting wire 12 c or the W-phase-to-U-phaseconnecting wire 13 c may be formed into a ring along the circumferentialdirection of the stator 3. Also, in addition to the U-phase-to-V-phaseconnecting wire 11 c, the V-phase-to-W-phase connecting wire 12 c andthe W-phase-to-U-phase connecting wire 13 c may be formed into ringsalong the circumferential direction of the stator 3.

As shown in FIGS. 14 and 15, all of the connecting wires 11 c, 12 c, 13c may be formed into rings along the circumferential direction of thestator 3. In the stator 3 shown in FIG. 14, the connecting wires 11 c,12 c, 13 c are connected to each other by a single connecting member 15.In the stator 3 shown in FIG. 15, the connecting wires 11 c, 12 c, 13 care connected to each other by three connecting members 15. Thestructure shown in FIG. 14 reduces the number of components in a casewhere connecting wires are connected via connecting members.

In the above embodiment, the connecting wires 11 c, 12 c, 13 c arearranged along the axial end face 3 a of the stator 3 at the connectionportions. However, the connecting wires 11 c, 12 c, 13 c may be arrangedalong the axial direction of the stator 3.

In the above embodiment, the joint portions P are located in upperportions of the connecting wires 11 c, 12 c, 13 c, that is, on a part ofthe stator 3 opposite from the axial end face 3 a. However, the jointportions P may be located elsewhere. The joint portions P may be locatedon sides of the connecting wires 11 c, 12 c, 13 c. In this case, laserbeam is radiated along a direction perpendicular to the axial directionof the stator 3 toward the connecting wires 11 c, 12 c, 13 c, so thatthe joint portions P are formed on the sides of the connecting wires 11c, 12 c, 13 c.

A through hole for welding may be formed in the arcuate portions 15 a ofeach connecting member 15.

In the above embodiment, the film removal process may be omitted, andthe film may be removed during the welding.

In the above embodiment, to improve the peel property of the film on theconnecting wires 11 c, 12 c, 13 c, laser absorption material (forexample, carbon black) may be mixed in or applied to the surface of theconnecting wires 11 c, 12 c, 13 c.

The winding process may be executed with the split core pieces 7 areannularly arranged such that distal ends of the tooth portions 8 a to 8l are directed axially outward.

In the above embodiment, the number of the split core pieces 7 formingthe stator core 6 is twelve. However, the number of the split corepieces 7 is not limited to twelve, but may be less or more than twelve.The number of the coils is changed in correspondence with the number ofthe split core pieces. Instead of forming the stator core 6 by the splitcore pieces 7, the stator core may be formed as an integral body.

In the above embodiment, two coils in each of the coil groups, or theU-phase coils U1 to U4, the V-phase coils V1 to V4, and the W-phasecoils W1 to W4, are wound about two tooth portions 8 adjacent to eachother in the circumferential direction of the stator 3, and theremaining two coils are wound about two tooth portions 8 spaced by 180°from one of the first two coils. This configuration may be changed. Forexample, the four coils of each phase may be wound about tooth portions8 such that the four coils are arranged at 90 degree intervals.

In the above embodiment, the same phase connecting wires 14 are formedon an end face of the stator 3 opposite from the end face on which thephase-to-phase connecting wires 11 c, 12 c, 13 c. However, the samephase connecting wires 14 may be formed on the same side as thephase-to-phase connecting wires 11 c, 12 c, 13 c.

In the above embodiment, the coils C are divided into three phases, butthe configuration is not limited to this. The coils C may be dividedinto n phases (n being a natural number greater then one).

In the above embodiment, the present invention is employed to connectthe connecting wires 11 c, 12 c, 13 c to each other. However, the use ofthe present invention is not limited to this. For example, presentinvention may be used to join the connecting wires 11 c, 12 c, 13 c toother conductive members (for example, terminals). Alternatively, thepresent invention may be used to join the power lines 11 a to 13 b (theends of lead wires forming the coils).

In the above embodiment, the connecting members 15 (or the holder 20)are not fixed to the stator core 6. However, the connecting members 15(or the holder 20) may be fixed to the stator core 6. Each connectingmember 15 (or the holder 20) is provided with projections, and groovesfor receiving the projections are formed in the insulator of the statorcore 6. The connecting members 15 (or the holder 20) is fixed to thestator core 6 by inserting each projection into the correspondinggroove. This structure allows the connecting wires 11 c, 12 c, 13 c(drawn wires) of the coils C to be easily welded and fixed, and improvesthe durability against external vibration.

As shown in FIG. 16, each connecting member 15 may be formed toencompass the U-phase-to-V-phase connecting wire 11 c and theV-phase-to-W-phase connecting wire 12 c (or the W-phase-to-U-phaseconnecting wire 13 c), which are arranged to contact each other. Eachconnecting member 15 electrically connects the U-phase-to-V-phaseconnecting wire 11 c and the V-phase-to-W-phase connecting wire 12 c (orthe W-phase-to-U-phase connecting wire 13 c), for example, by fusing.

Each connecting member 15 is a two-wire connecting member that connectsthe single U-phase-to-V-phase connecting wire 11 c with the singleV-phase-to-W-phase connecting wire 12 c (or with W-phase-to-U-phaseconnecting wire 13 c). However, the present invention is not limited tothis. For example, each connecting member 15 may be three-wireconnecting member. In this case, the V-phase-to-W-phase connecting wire12 c is bent, and a part of the connecting wire 12 c that is drawn fromthe W-phase coil W4 and a part of the connecting wire 12 c that is drawnfrom the V-phase coil V3 are arranged to overlap each other. These twowires and the U-phase-to-V-phase connecting wire 11 c are connectedtogether by the connecting member 15.

In the above embodiment, the connecting wires 11 c, 12 c, 13 c areconnected together by the connecting members 15 on the coils C. However,for example, the connecting wires 11 c, 12 c, 13 c may be connected toconnection terminals held by the holder member 5. In this configuration,the connecting wires 11 c, 12 c, 13 c can be separated from the coils C.This improves the electrical insulation between the connecting wires 11c, 12 c, 13 c and the coils C.

1. A stator comprising: a stator core that includes a plurality of splitcore pieces each having a tooth portion, the split core pieces beingannularly arranged such that distal ends of the tooth portions faceradially inward; and a plurality of coils each wound about one of thetooth portions, the coils are divided into groups of n phases; wherein alead wire is continuously wound about an adjacent pair of the toothportions such that coils of different phases are formed in thecircumferentially adjacent tooth portions, so that a plurality ofconnecting wires are provided, each connecting wire connecting coils ofdifferent phases, and wherein either the connecting wires are connectedto each other or the connecting wires are connected to each other in astate where at least one of the connecting wires is cut, such that aneutral point is created.
 2. The stator according to claim 1, wherein atleast one of the connecting wires is formed into a ring extending alongthe circumferential direction of the stator.
 3. The stator according toclaim 2, wherein the coils include a U-phase coil, a V-phase coil, and aW-phase coil, and wherein the connecting wires include aU-phase-to-V-phase connecting wire connecting the U-phase coil and theV-phase coil, a V-phase-to-W-phase connecting wire connecting theV-phase coil and the W-phase coil, and a W-phase-to-U-phase connectingwire connecting the W-phase coil and the U-phase coil.
 4. The statoraccording to claim 3, wherein at least one of the U-phase-to-V-phaseconnecting wire, the V-phase-to-W-phase connecting wire, and theW-phase-to-U-phase connecting wire is formed into a ring extending alongthe circumferential direction of the stator.
 5. The stator according toclaim 3, wherein one of the U-phase-to-V-phase connecting wire, theV-phase-to-W-phase connecting wire, and the W-phase-to-U-phaseconnecting wire is formed into a ring extending along thecircumferential direction of the stator.
 6. The stator according toclaim 3, wherein at least one of the U-phase-to-V-phase connecting wire,the V-phase-to-W-phase connecting wire, and the W-phase-to-U-phaseconnecting wire is arched and extends to a circumferentially adjacentone of the connecting wires.
 7. The stator according to claim 3, whereintwo of the U-phase-to-V-phase connecting wire, the V-phase-to-W-phaseconnecting wire, and the W-phase-to-U-phase connecting wire are archedand extend to the other connecting wire, and wherein theU-phase-to-V-phase connecting wire, the V-phase-to-W-phase connectingwire, and the W-phase-to-U-phase connecting wire are electricallyconnected to one another by a single connecting member.
 8. The statoraccording to claim 3, wherein the connecting wires extend substantiallyparallel with an end face of the stator in the axial direction, whereinthe connecting wires are electrically connected to one another bywelding or the connecting wires and other conductive members areelectrically connected to each other by welding, and joint portionsformed by the welding are located in a part of the connecting wires orof said other conductive members, which part does not face the end faceof the stator in the axial direction.
 9. The stator according to claim8, wherein the joint between the connecting wires or the joint betweenthe connecting wires and said other conductive members is achieved byconnecting members at the joint portions.
 10. The stator according toclaim 8, wherein the connecting wires and the connecting members arejoined by laser welding.